netdev - Re: kernel panic in skb_copy

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Date:	Mon, 01 Jul 2013 09:29:02 +0100
From:	Alex Bligh <alex@...x.org.uk>
To:	Joe Jin <joe.jin@...cle.com>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Frank Blaschka <frank.blaschka@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	zheng.x.li@...cle.com, Xen Devel <xen-devel@...ts.xen.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Jan Beulich <JBeulich@...e.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Alex Bligh <alex@...x.org.uk>
Subject: Re: kernel panic in skb_copy_bits

Joe,

> Do you know if have a fix for above? so far we also suspected the
> grant page be unmapped earlier, we using 4.1 stable during our test.

A true fix? No, but I posted a patch set (see later email message
for a link) that you could forward port. The workaround is:

>> A workaround is to turn off O_DIRECT use by Xen as that ensures
>> the pages are copied. Xen 4.3 does this by default.
>>
>> I believe fixes for this are in 4.3 and 4.2.2 if using the
>> qemu upstream DM. Note these aren't real fixes, just a workaround
>> of a kernel bug.
>
> The guest is pvm, and disk model is xvbd, guest config file as below:
...
> I think this only for pvhvm/hvm?

I don't have much experience outside pvhvm/hvm, but I believe it
should work for any device.

Testing was simple - just find all (*) the references to O_DIRECT
in your device model and remove them!

(*)=you could be less lazy than me and find the right ones.

I am guessing it will be the same ones though.

-- 
Alex Bligh
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